This invention relates generally to smelting furnaces and to the production of steels, and more particularly to a furnace for producing steels with steel scrap and the like as a raw material.
It is well known that the furnace wall of a furnace for melting metal must have excellent thermal properties such as heat resistance, heat insulation, high strength at high temperature, and erosion resistance similarly as in the case of ordinary heating furnaces. However, in a steel producing furnace, particularly that wherein steel is produced with steel scrap as a raw material, a high concentration of thermal energy is applied to the furnace thereby to elevate the working efficiency, and for this reason, the temperature of the interior of the furnace rises to a very high value.
Consequently, the firebricks lining the furnace tend to be damaged severely, and hence frequent maintenance (or periodical repairs) and replacement of the firebricks are required. Furthermore, even during operation, spalling and erosion caused by the spattering of oxidized metal have frequently and unavoidably made it necessary to interrupt the operation of the furnace at time, other than those for periodical maintenance. Frequent interruptions of furnace operation reduces the steel quantity thereby produced, and hence elevates the production cost.
In order to avoid the above described difficulties in the known furnaces, use is made of improved bricks such as basic high burned bricks and the like, which are baked at a higher temperature than the ordinary firebricks. However, so far as we are aware, none of these firebricks could satisfactorily overcome the aforementioned difficulties of the conventional furnaces.
It is also known that so-called carbonaceous bricks have a softening temperature in a range of from 1,500.degree. C to 1,900.degree. C, and the heat resistance thereof is far superior to those of any of the conventional firebricks. Furthermore, the real density of a carbonaceous brick is approximately 3,000 kg/m.sup.3, which is much higher than those of other bricks, and the specific heat thereof is 0.2 Kcal/kg.degree.C. A carbonaceous brick also has high strength at high temperatures, and the resistance thereof to spalling is much higher than those of the ordinary firebricks.
However, a carbonaceous brick has drawbacks such as high susceptivity to oxidation, and low resistance to slag attack at high temperatures. In addition, the thermal conductivity of the carbonaceous brick is almost ten-times higher than that of the ordinary firebricks. These disadvantageous properties of carbonaceous bricks are so significant that it has been considered heretofore that carbonaceous bricks are not suitable for furnace walls despite the aforementioned advantageous features.